This invention relates generally to intrusion detection devices. More particularly, my invention relates to an infrared sensing system for detecting the presence of objects between two areas being scanned. The invention is of particular importance to the elevator industry and is primarily designed for elevators.
In the prior art it has long been recognized to sense for intrusion within specified areas through various optical systems involving the establishment and detection of light pathways. There are many applications requiring sensing of the presence of objects or intrusions between structural areas. Automatic elevator doors, which automatically slide between opened and closed positions, are a prime example. Numerous attempts have been made in the prior art to make the doors "safe" and to provide reliable means for sensing the presence of passengers or obstacles between the doors. Numerous mechanical devices have been proposed for controlling the doors and withdrawing pressure in response to predetermined forces, and numerous systems for electrically monitoring doors have also been proposed. Reflected energy receivers are seen in U.S. Pat. No. 4,669,218. A simple gate operated in response to light beams is seen in U.S. Pat. No. 4,472,908, issued Sep. 25, 1984. This device controls a pair of swinging gates with a light path which may be broken by an intruder.
Trett U.S. Pat. No. 4,894,952 discloses a proximity detection system for sensing obstructions in the path of the door. An array of transmitter-receiver pairs transmit infrared energy downwardly in a confined space and looks for reflections to determine the presence of a passenger. In Glonet U.S. Pat. No. 4,914,859 a plurality of object presence sensing detectors involving ultrasonic transducers are placed along the pathway of a pair of elevator doors to sense for passengers.
Pronovost U.S. Pat. No. 3,746,863 discloses a switched network controlling a light curtain established between a pair of vertical members through which passengers may move. Pairs of receivers and transmitters alternate between the vertical points defining the gate, and means are provided for logically determining the presence or absence of an intruder. Haag U.S. Pat. No. 4,742,337 provides a system wherein light may be transmitted from a receiving transmitting strip towards an area to be monitored. Light is returned through the area from a reflective strip, and the absence of a return indicates the presence of an intruder.
Trett U.S. Pat. No. 4,910,464 issued Mar. 20, 1990 discloses a proximity detection system ideally for use with sliding elevator doors. An array of transmitter receiver pairs transmit energy across the doorway, expecting to receive a return reflection from the opposite doorway.
Scoville U.S. Pat. No. 3,852,592 discloses a door monitoring system involving infrared radiation which is broadcast in a detection zone immediately in front of the doorway. A three dimensional control zone is set up through scanning arrays, but the system is activated with reflective light. A photoelectric intruder device disclosed in U.S. Pat. No. 3,719,938 photoelectrically illuminates a particular area, and indicates an intrusion in response to predetermined reflection conditions.
Mills U.S. Pat. No. 4,029,176 discloses a proximity sensing system for elevator doors that transmits bursts of acoustic energy across the doorway to define a three dimensional sensing space. Timing intervals are employed to interpret reflected information.
U.S. Pat. No. 3,965,355 issued Jun. 22, 1976 discloses an infrared laser system which transmits light across a path to detect obstructions or intrusions.
Federmann U.S. Pat. No. 3,370,677 issued Feb. 27, 1968 discloses a proximity sensing system adapted to be disposed within sliding elevator doors. The field transmitted by the moving door is electrostatic, and in response to the variance of the field in response to an intruder or passenger, capacitance changes sensed by an analog circuit determine presence. Weber U.S. Pat. No. 4,266,124, Issued May 5, 1981 discloses a system wherein a plurality of infrared sources are strobed sequentially and transmitted across a space to be received by cooperating receivers.
One of the most relevant patents known to me is U.S. Pat. No. 4,794,248, issued Dec. 27, 1988. The latter reference discloses a system adapted to be employed on two sliding elevator doors. A plurality of infrared transmitters are disposed on vertically spaced apart locations on both doors. A receiving sensor is disposed on the top and bottom of each door, for sequentially monitoring radiation transmitted across the gap. The presence of an object in the pathway is detected when a radiant pathway is broken. The transmitters are energized sequentially. It is unclear how or what the logic circuit does, but the point is to try and detect intrusions by establishing and monitoring radiation pathways. Receivers and transmitters are not arranged in separate vertical columns as I have proposed, and no disclosure of a sophisticated digital logic sensing system is made in the latter reference.
U.S. Pat. No. 3,886,413 issued May 27, 1975 discloses a presence sensing system having a self checking diagnostic operation. The system provides indications of normal, intrusion, withdrawal conditions within guarded zone within a machine for safety purposes.
However, even in the case of reasonably sophisticated infrared sensing systems for use in the elevator arts, a number of problems remain. Slowness is a well known detriment. Also, infrared sensing devices of previous designs known to me have hitherto required repetitive servicing. As the elevator continues to be used various parts are subject to strain and normal wear and tear. Doors may often be subject to partially damaging collisions with hospital cars or the like, and sometimes critical parts are jarred out of alignment. Service calls and down time usually result. Moreover, because of the numerous ages and demeanors of people using elevators, and the frequency of vandalism, items of litter may randomly and periodically block pathways. It is not uncommon for gum and cigarette butts to be thrust into important radiation paths which can disable sensing equipment and necessitate a service call. Because of the relative simplicity of earlier elevator sensing systems, minor acts of vandalism aggravate down time and increase the necessity for service calls, much to the dismay and detriment of the building operators.
A significant weakness in earlier systems is that they do not automatically vary their radiation sensing patterns in response to semi-permanent mechanical blockage of beam pathways. In other words, when a preestablished sensing pathway is blocked, the circuit inflexibly indicates an intrusion, and the elevator doors are held open. The door sensing system can thus be sabotaged and rendered useless when a child places some gum on the wrong part of the door. If a system establishes redundant light pathways to reliably check for intrusions, it can reliably operate with less than all of its pathways operational. I have determined that the circuitry should actively modify its expected pathway sensing information to adjust itself to adapt for minor vandalism.
To speed up elevator operation I have found that it is extremely advantageous to vary the radiation pattern in accordance with the spacing of the doors. The logic must be able to differentiate between "wide" and "narrow" stances, and at the same time the logic must be capable of adequate diagnostics to please the service personnel. Moreover, in response to a mechanical change or blockage in the radiation pathway the system should be able to adapt and "learn" the new radiation patterns to operate properly without obstructing, delaying, or aggravating passengers. Whether sensing long or short distances, it must assume, determine, and operate under its new logic infrared sensing pattern.